Trouble importing STL produced by VTK
The import goes fine, but the model isn't visible in the viewport because the view isn't pointing at it, you could do a few things:  


zoom out  (mouse wheel)
rotate the view. (middle mouse button)
press home to View All.

Use the Outliner View to see if the object imported, then select the object by clicking the name.

With the mouse cursor in the 3D View press . (period) to focus the view on the selected object.